netdev - Re: [PATCH bpf-next 3/3] selftests/bpf: Add tests for get_func_[arg|ret|arg

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Date:   Wed, 8 Dec 2021 17:38:14 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Andrii Nakryiko <andriin@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH bpf-next 3/3] selftests/bpf: Add tests for
 get_func_[arg|ret|arg_cnt] helpers

On Tue, Dec 07, 2021 at 02:54:33PM -0800, Andrii Nakryiko wrote:

SNIP

> > > > +__u64 test1_result = 0;
> > > > +SEC("fentry/bpf_fentry_test1")
> > > > +int BPF_PROG(test1)
> > > > +{
> > > > +   __u64 cnt = bpf_get_func_arg_cnt(ctx);
> > > > +   __u64 a = 0, z = 0, ret = 0;
> > > > +   __s64 err;
> > > > +
> > > > +   test1_result = cnt == 1;
> > > > +
> > > > +   /* valid arguments */
> > > > +   err = bpf_get_func_arg(ctx, 0, &a);
> > > > +   test1_result &= err == 0 && (int) a == 1;
> > >
> > >
> > > int cast unnecessary? but some ()'s wouldn't hurt...
> >
> > it is, 'a' is int and trampoline saves it with 32-bit register like:
> >
> >   mov    %edi,-0x8(%rbp)
> >
> > so the upper 4 bytes are not zeroed
> 
> oh, this is definitely worth a comment, it's quite a big gotcha we'll
> need to remember


ok, will add comment for that

jirka

> 
> 
> >
> > >
> > >
> > > > +
> > > > +   /* not valid argument */
> > > > +   err = bpf_get_func_arg(ctx, 1, &z);
> > > > +   test1_result &= err == -EINVAL;
> > > > +
> > > > +   /* return value fails in fentry */
> > > > +   err = bpf_get_func_ret(ctx, &ret);
> > > > +   test1_result &= err == -EINVAL;
> > > > +   return 0;
> > > > +}
> > > > +
> > > > +__u64 test2_result = 0;
> > > > +SEC("fexit/bpf_fentry_test2")
> > > > +int BPF_PROG(test2)
> > > > +{
> > > > +   __u64 cnt = bpf_get_func_arg_cnt(ctx);
> > > > +   __u64 a = 0, b = 0, z = 0, ret = 0;
> > > > +   __s64 err;
> > > > +
> > > > +   test2_result = cnt == 2;
> > > > +
> > > > +   /* valid arguments */
> > > > +   err = bpf_get_func_arg(ctx, 0, &a);
> > > > +   test2_result &= err == 0 && (int) a == 2;
> > > > +
> > > > +   err = bpf_get_func_arg(ctx, 1, &b);
> > > > +   test2_result &= err == 0 && b == 3;
> > > > +
> > > > +   /* not valid argument */
> > > > +   err = bpf_get_func_arg(ctx, 2, &z);
> > > > +   test2_result &= err == -EINVAL;
> > > > +
> > > > +   /* return value */
> > > > +   err = bpf_get_func_ret(ctx, &ret);
> > > > +   test2_result &= err == 0 && ret == 5;
> > > > +   return 0;
> > > > +}
> > > > +
> > > > +__u64 test3_result = 0;
> > > > +SEC("fmod_ret/bpf_modify_return_test")
> > > > +int BPF_PROG(fmod_ret_test, int _a, int *_b, int _ret)
> > > > +{
> > > > +   __u64 cnt = bpf_get_func_arg_cnt(ctx);
> > > > +   __u64 a = 0, b = 0, z = 0, ret = 0;
> > > > +   __s64 err;
> > > > +
> > > > +   test3_result = cnt == 2;
> > > > +
> > > > +   /* valid arguments */
> > > > +   err = bpf_get_func_arg(ctx, 0, &a);
> > > > +   test3_result &= err == 0 && (int) a == 1;
> > > > +
> > > > +   err = bpf_get_func_arg(ctx, 1, &b);
> > > > +   test3_result &= err == 0;
> > >
> > >
> > > why no checking of b value here?
> >
> > right, ok
> >
> > >
> > > > +
> > > > +   /* not valid argument */
> > > > +   err = bpf_get_func_arg(ctx, 2, &z);
> > > > +   test3_result &= err == -EINVAL;
> > > > +
> > > > +   /* return value */
> > > > +   err = bpf_get_func_ret(ctx, &ret);
> > > > +   test3_result &= err == 0 && ret == 0;
> > > > +   return 1234;
> > > > +}
> > > > +
> > > > +__u64 test4_result = 0;
> > > > +SEC("fexit/bpf_modify_return_test")
> > > > +int BPF_PROG(fexit_test, int _a, __u64 _b, int _ret)
> > > > +{
> > > > +   __u64 cnt = bpf_get_func_arg_cnt(ctx);
> > > > +   __u64 a = 0, b = 0, z = 0, ret = 0;
> > > > +   __s64 err;
> > > > +
> > > > +   test4_result = cnt == 2;
> > > > +
> > > > +   /* valid arguments */
> > > > +   err = bpf_get_func_arg(ctx, 0, &a);
> > > > +   test4_result &= err == 0 && (int) a == 1;
> > > > +
> > > > +   err = bpf_get_func_arg(ctx, 1, &b);
> > > > +   test4_result &= err == 0;
> > >
> > >
> > > same, for consistency, b should have been checked, no?
> >
> > ok
> >
> > thanks,
> > jirka
> >
>